First observation of ϕ-meson mass modification in nuclear medium

R. Muto, J. Chiba, H. En'yo, Y. Fukao, H. Funahashi, H. Hamagaki, M. Ieiri, M. Ishino, H. Kanda, M. Kitaguchi, S. Mihara, K. Miwa, T. Miyashita, T. Murakami, T. Nakura, M. Naruki, M. Nomachi, K. Ozawa, F. Sakuma, O. SasakiH. D. Sato, M. Sekimoto, T. Tabaru, K. H. Tanaka, M. Togawa, S. Yamada, S. Yokkaichi, Y. Yoshimura

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


We have measured e+ e- invariant mass spectra in 12 GeV p + A interactions at the KEK Proton-Synchrotron. The aim of the experiment is to detect possible in-medium modification of vector mesons at normal nuclear density. We used carbon and copper targets to study the nuclear size dependence of the e+ e- invariant mass spectra. A significant enhancement on the low-mass side of the φ{symbol} meson peak was observed in the low βγ region (β γφ{symbol} < 1.25) in the copper data. On the other hand, in the higher βγ region (β γφ{symbol} > 1.25), both the spectral shapes obtained from carbon and copper targets were consistent with the expected one from the simulation. This observation is consistent with a picture of the φ{symbol} modification in a nucleus, i.e. normal nuclear density, because such an effect should be visible only for slowly moving mesons produced in a larger nucleus.

Original languageEnglish
Pages (from-to)723-726
Number of pages4
JournalNuclear Physics A
Issue number1-4
Publication statusPublished - 2006 Aug 7
Externally publishedYes

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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